**Core Concept**
The concentration of ethyl alcohol in blood and urine is an important consideration in forensic toxicology and clinical settings. The ratio between blood and urine ethyl alcohol concentrations is influenced by factors such as hydration status, kidney function, and the rate of alcohol metabolism.

**Why the Correct Answer is Right**
The correct ratio between blood and urine ethyl alcohol concentration is 1:10 to 1:20. This is because the kidneys filter and concentrate the alcohol from the blood, resulting in a higher concentration in the urine. However, the exact ratio can vary depending on individual factors such as hydration status and renal function. The kidneys can concentrate the alcohol to a greater extent in individuals who are well-hydrated, resulting in a higher urine-to-blood ratio.

**Why Each Wrong Option is Incorrect**
* **Option A:** This option is incorrect because the ratio between blood and urine ethyl alcohol concentration is not 1:1. The kidneys filter and concentrate the alcohol from the blood, resulting in a higher concentration in the urine.
* **Option B:** This option is incorrect because the ratio between blood and urine ethyl alcohol concentration is not 1:5. While the kidneys do concentrate the alcohol from the blood, the exact ratio can vary depending on individual factors.
* **Option C:** This option is incorrect because the ratio between blood and urine ethyl alcohol concentration is not 1:50. While this option may seem plausible, it is not supported by scientific evidence.

**Clinical Pearl / High-Yield Fact**
A useful mnemonic to remember the ratio between blood and urine ethyl alcohol concentration is "10:1, not 1:1." This highlights the importance of considering the concentrating effect of the kidneys when interpreting urine alcohol concentrations.

**Correct Answer: A. 1:10 to 1:20**